<html><head><title>RangeFinder Help</title></head>
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This tool can help you estimate the distance to an object.  It is based on
the disparity between what each of your eyes sees.  To use it, hold it at arm's
length, close your right eye and align the left edge of the display with the
object of interest.  Then hold the device still, switch eyes and move the red line
(using the touch screen, buttons, or trackball) so that it also aligns with the object.
You can switch eyes a few times to verify the two lines still lineup with the object.
Then you can read off the calculated distance.<p>

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<tr><td><img src=rangefinderexample.png></td>
<td>The amount of disparity between what your two eyes see differs with the distance to the object you're looking at.  By measuring the disparity, the distance can be estimated</td></tr></table>

In order for this to be accurate, you must enter the distance between eyes (pupil-to-pupil)
and the distance between your eyes and the device (about shoulder to base of thumb).  Your device
also needs to properly report its screen dimensions.  If the ruler displayed at the bottom
of the screen does not look correct, then your device probably isn't reporting it correctly.<p>

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<td><img src=smallchart.png></td></tr>
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Due to the way this measurement is set up, the accuracy degrades at further distances.
This graph shows the an eye separation of 6.6cm and an arm length of 60cm, and you can see its asymptotic behavior as visual displacement approaches eye separation.
There may also be error from mismeasuring eye separation or arm length or holding the device at different distances.  Beyond about 30m, error may be unacceptably high.
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<font color=#888888>Copyright 2010 Google Inc.</font>
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